No abstract

SUMMARY Changes in the lipids of soybeans brought about by Rhizopus orysae during the production of tempeh were studied. The mold possesses strong lipase activity and caused the hydrolysis of over one‐third of the neutral fat of the soybean during the three‐day fermentation. The fatty acid composition of soybean tempeh was compared with that of cooked soybeans by vapor‐phase chromatography of the methylesters. The neutral fat was composed of palmitic, stearic, oleic, linoleic, and linolenic acids, with linoleic acid predominating. These acids were liberated during fermentation in roughly the same proportions found in soybeans after heating 90 min at 100°C. During the most active mold growth, proportionately higher levels of palmitic acid were found, and the level of linoleic acid was somewhat lower. Except for the depletion of some 40% of the linolenic acid in the later stages of the fermentation, there apparently was no preferential utilization of any fatty acid.

This study is focused on the characterization of the interaction of the amphiphilic peptide bombolitin III (from the bumblebee Megabombus pennsylvanicus) with phospholipid monolayers and vesicles. It is shown that due to the amphiphilic character of its alpha-helical conformation this water-soluble peptide is able to interact in an ordered fashion with phospholipid organized structures. Depending on the temperature, the subphase, and the particular phosphatidylcholine used, the mixed peptide-phospholipid monolayers can be homogeneous or display phase separation. This behavior was observed by means of the Langmuir film balance technique, coupled with an epifluorescence microscope. In well-defined conditions it is possible to visualize the formation of phase-separated peptide domains at the air-water interface and to study the effect of their presence on the organization of the lipid. The action of phospholipase A2 at the lipid-peptide interface was also followed by means of fluorescence microscopy: some evidence that the enzyme preferentially hydrolyzes the phospholipid that is in contact with the peptide is presented. Furthermore, the presence of bombolitin III in L-alpha-DLPC monolayers causes an increase in the initial speed of degradation with phospholipase A2. These results are in agreement with previous findings that show that the bombolitins are activators in vitro of phospholipase A2. Experiments were also performed with peptide fragments corresponding to the alpha-helical sequences of the protein uteroglobin: despite some amphiphilic character, these peptides do not interact strongly with phospholipid monolayers. Only one of these peptides (corresponding to the helix 4-14 in uteroglobin) is adsorbed in the monolayer in a similar fashion to bombolitin III but does not cause an increase in the activity of phospholipase A2.